This invention relates to radiation-emitting devices.
Currently available radiation-emitting devices, such as a display, take various different forms. In cathode-ray tube displays (CRT's) electrons produced by a source are accelerated by an applied voltage across a vacuum onto a phosphor screen. The beam of electrons is scanned over the screen magnetically or electrostatically, to produce the desired display representation. CRT's suffer from various disadvantages. They require high drive voltages, they are relatively bulky and are not very robust.
Alternative displays generally comprise a matrix array of light-emitting or reflecting devices, such as light-emitting diodes or liquid crystal elements. These can provide more compact and robust displays than CRT's but also suffer from various disadvantages such as relatively slow response times, lower resolution, reduced visibility or limited viewing angle.
In GB 2252857 there is described a solid-state display comprising a glass plate on which is deposited an upper layer of parallel conductive tracks interrupted by recesses containing a conductive or semiconductive phosphor. An array of vertical ballistic transistors within a semiconductor layer is in alignment on one side with the phosphor regions and on the other side with respective conductive tracks which extend at right angles to the tracks in the upper layer. When a voltage is applied to one of the tracks in the upper layer which is positive with respect to the voltage applied to one of the lower tracks, it causes one of the transistors to emit electrons upwardly into the phosphor region. This causes fluorescence of the region and the emission of light.
While this form of display can be used satisfactorily for normal viewing by the unaided eye, there are circumstances where an improved resolution and maximum radiation flux are required such as, for example, where images need to be formed in printing devices.